Organic electroluminescence display device

ABSTRACT

The strength of the whole OLED is increased by proposing a new method of fixing OLED panels. To address the problem, an OLED element is formed on a substrate, and a sealing substrate of a structure by which the substrate is sealed is fixed to a lower metallic frame via an elastic sheet. Silicon resin is preferably used as the sheet, and use of a sheet having a heat diffusion function based on radiation is more desirable.

CLAIM OF PRIORITY

The present application claims priority from Japanese Application JP2006-051333 filed on Feb. 27, 2006, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the housing structure of an organic ELdisplay device.

2. Description of the Related Art

As one of display devices, an organic EL display device (hereinafterreferred to as OLED) has the following characteristics:

1. A display element constituting the OLED is a self light emittingelement that does not require backlight.

2. Wide viewing angle and high visibility

3. The high response speed enables high-quality display withoutdifference between moving images and static images.

4. Direct-current, low-voltage driving is enabled.

Therefore, the OLED is expected to contribute to applications formobile/portable equipments having severe power requirements, and makingtelevision and notebook size personal computers thin and light inweight. In the present situation, since there are a small number ofcommercially available products provided with the OLED, the housingstructures of OLEDs, including those that use resin frames for LCDpanel, are classified as follows.

(1) Bonding the OLED to frames and fixing the upper and lower frames bycircular dowels (spherical projections)

(2) Fixing resin frames for LCD to the OLED

Because of the structure that a display element constituting the OLED isa self light emitting element, since backlight in a liquid crystaldisplay device (LCD) is not required, the OLED also does not requireresin mold parts supporting the backlight structure, it has productadvantages such as thin size, light weight, and low costs.

The method described in (1) has the following problem. That is, althoughdouble-faced tape is usually used for this kind of fixing, sincesticking the double-faced tape to an OLED element requires adhesive orthe like, the adhesive inevitably deteriorates with time, and there is aproblem of reliability attributable to deterioration in the adhesive dueto heat generation. In the fixing of the upper and lower frames, becauseof engagement assembly by circular dowels, both assembly precision andassembly rigidity are low because of slip in engagement portions of thedowels.

The method described in (2) also has the following problem. That is,although the rigidity of the element can be obtained by fixing to aresin mold, dies for manufacturing the resin mold are more expensivethan those for metallic frames. To obtain higher rigidity by the resinmold, a display element becomes thicker as a whole, and its externalsize becomes larger, greatly reducing attraction of a product.

An OLED of the bottom emission method has the following problem. Thatis, the OLED of the bottom emission method has connection terminals of aflexible printed circuit substrate (FPC) and the like in the reverseside of the light emitting surface of a display element. Therefore, whenthe OLED has been placed in the housing, since flat cables of the FPCand the like, when connected to a driving circuit, are bent in thedirection that peels the surface of flat cable bonding to the OLED,there is a problem in ensuring reliability.

However, since the OLED is structured to have no resin mold, there is aproblem in impact resistance and torsion resistance. Therefore, toensure the structure reliability of the OLED, a frame structure formaintaining the strength of the OLED is an indispensable factor.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an organicelectroluminescence display device that ensures structural reliabilityof the OLED.

As a means for addressing the above-described object, an OLED element isformed on a substrate, and a sealing substrate of a structure by whichthe substrate is sealed is fixed to a lower metallic frame via anelastic sheet. Although the elastic sheet is preferably silicon resin,common double-faced tape is also an effective means because it iselastic. By providing the elastic sheet with a function such as heatdiffusion, the reliability of the OLED element can be increased.

Although not a method of fixing an OLED, the following means isavailable to increase frame strength. That is, a lower frame and anupper frame are provided with an engagement structure (snap fit) havinga notch shape to prevent positional deviation in the thickness directionafter assembly.

By designing the snap fit part in each side, positional deviation inthickness direction and vertical direction, that is, lateral directionand rotation direction can be suppressed as the whole frame.

The following structure helps to increase heat radiation effects. Thatis, by designing wall parts with an upper frame and a lower framecombined apart from OLED panels, impact strength and static loadstrength can be increased in comparison with an OLED panel unit. Sincean air path is formed within an OLED element structure, temperaturedistribution can be properly maintained, and cooling efficiency isincreased.

A slope spring is provided in the lower frame and a support spring isprovided in the upper frame. In this case, the height of the jointsurface of the upper and the lower springs is designed to be nearer tothe light emitting surface than the position of the surface of FPCextraction to the OLED. As a result, in whatever direction flat cablesof the FPC and the like are bent, no force occurs in the direction thatpeels from the surface of bonding to the OLED element. Therefore, thereliability of connection of the flat cables of the FPC and the like tothe OLED is increased. By this construction, when the slope spring isprovided in the lower frame, the effect of correcting the position inwhich the OLED is mounted can be obtained. As a result, the precision ofOLED mounting position is increased, and positional deviation andinclination of the display surface of the OLED can be preciselymanufactured.

According to the present invention, the reliability of the organic ELdisplay device can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional structure of a general OLED;

FIG. 2 shows a sectional structure of an OLED sealed by a sealing glasssubstrate;

FIG. 3 is a structural drawing of an OLED element of the presentinvention that uses a frame structure;

FIG. 4 shows a truss structure part of this proposal;

FIG. 5 shows a conventional doweling-based frame assembly method;

FIG. 6 shows an example of positional deviation in a doweling part;

FIG. 7 is a drawing showing FPC peel stress induced by FPC bending;

FIG. 8 shows the spring support structure of FPC;

FIG. 9 shows a peel stress suppressing mechanism of FPC;

FIG. 10 shows a mechanism of infrared absorption and an elastic (buffer)film;

FIG. 11 shows a bending stress absorbing mechanism by an elastic(buffer) film; and

FIG. 12 is a structural drawing of an OLED panel showing space allocatedin the outer regions of OLED.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

First Embodiment

FIG. 1 shows a sectional structure of a general OLED. Since the OLEDshown in FIG. 1 has a structure conventionally know, a detaileddescription of it is omitted. In FIG. 1, a light emitting surface is ina lower side, and an organic light-emitting layer and a cathode metalare formed via an optically transparent multilayer film about 1 μm froma substrate glass. This structure is called an OLED of a bottom emissionmethod. An OLED of this structure generally has a desiccant and an emptywall in the reverse side of a light emitting part, and is sealed by asealing glass (or metal such as a sealing can) from externalatmospheres.

FIG. 2 shows a sectional structure of the OLED sealed by a sealing glasssubstrate. In the OLED sectional structure shown in FIG. 2, airtightness is maintained by the empty wall (generally space filled withnitrogen), the desiccant, and the sealing glass to extract heatgenerated in a structure part of the OLED from the back surface of thelight emitting surface. The whole thickness of the OLED with thesubstrate glass and the sealing glass laminated is about 1.0 mm, and theexistence of the empty wall within a display element poses the problemof maintaining strength against stress and impact from the outside.

<1. Making OLED Frames Highly Rigid>

As a countermeasure against stress and impact from the outside, an OLEDelement structure having a frame structure as shown in FIG. 3 to achievehigh rigidity has been developed. When a snap fitting part shown in FIG.3 is enlarged, it will be appreciated that an assembly section of anupper frame and a lower frame forms a truss structure (triangularsection). This is a characteristic of this proposal. The truss structureis a building method known conventionally in terms of structuralmechanics as a set of triangular shapes designed on side walls toimprove the strength of bridges. In recent years, a set of triangularsections, a so-called truss structure, is used as a design method forobtaining the strength of ceiling structure of large-scale domefacilities.

FIG. 4 shows a truss structure part of this embodiment. By designingsuch a truss structure (triangular sectional shape) on frame sides, whenstress is applied in the direction of compression from a verticaldirection of FIG. 4, elements on each side of a triangular section bythe truss structure disperse the stress in a direction of compression orextension. As a result, compression rupture strength increases aboutfour or more times in comparison with when frames are simply combined.

<2. Making OLED Frames Highly Precise>

As shown in FIG. 4, a joint part of the truss structure is designed tosupport a side of a lower frame at an about horizontal support angle atone side of a triangular element designed on an upper frame. Therefore,in FIG. 4, downward positional deviation of the lower frame will notoccur. Furthermore, upward positional deviation of the lower frame willnot occur because of the constraint of the thickness of an OLED paneland the existence of the vertex parts of truss structure, that is,contact parts between bending parts of the upper frame and edges of thelower frame. As a result, assembly precision of fitted portionsincreases, so that manufacturing precision as the whole OLED panelincreases.

On the other hand, with metallic frames of a conventional doweling(spherical section) method, since positional deviation occurs readily ina doweling part, assembly precision is very low (see FIGS. 5 and 6).

<3. Problem Peculiar to OLED of Bottom Emission Method>

An OLED of bottom emission method has a structure that a connectionsurface of flat cables of FPC and the like for OLED elements exist atthe reverse side of a light emitting surface. Therefore, when handlingan OLED module, depending on the direction that bends the FPC, stressmay occur in the direction that peels the FPC from the OLED elements.See FIG. 7. Therefore, one conceivable idea is to reinforce a connectionportion between the OLED elements and the FPC. However, in thisproposal, a countermeasure is taken against stress in a peel directionacting on the connection portion between the OLED elements and the FPCby designing a support spring mechanism in the upper and the lowerframes.

Furthermore, by providing a gradual inclination for the support springdesigned in the lower frame, it becomes possible to provide aself-alignment mechanism for mechanically correcting a positionaldeviation when fixing the OLED elements to the frame, contributing to anincrease in assembly precision as an OLED module structure (see FIGS. 8and 9).

<4. Stress Buffering Mechanism when Bending Stress is Applied>

With consideration to the handling of a delivered product and actual usestates in a final customer, it is necessary to make a design for theapplication of accidental impact and stress. In this embodiment, anelastic special film, a silicon resin film 0.2 mm thick, is used when anOLED is fixed to a lower frame. As a result, even when the frame is bentwith bending stress applied to an OLED module, it has become possiblethat the elastic film buffers the stress to protect the OLED elements.In comparison with a conventional method of fixing by double-faced tape,as tolerance for bending stress, bending rupture strength by the elasticfilm stands at 250 or more against 100 for bending rupture strength bydouble-faced tape, indicating a significant increase in strength (seeFIGS. 10 and 11).

Furthermore, by allocating a space between the OLED and the inner wallof the frames by a predetermined amount or more, ideally 50% or moreof-the whole thickness of the OLED, when impact by drop or the like isapplied from the outside, the impact is absorbed to buffer the impact,or the space portion is deformed to absorb the impact, resulting in theprevention of the OLED elements from destruction. Stress occurring whenthe OLED module is fixed to a housing in a customer can also be absorbedin the space portion (see FIG. 12).

<5. Heat Diffusion Mechanism of OLED>

Since an OLED is a spontaneous light emitting element, its lightemitting operation generates heat. Although the heat generation exertsno influence on reliability in room temperature environments, anincrease in temperatures caused by heat generated in the OLED must beminimized in severely hot environments. In this embodiment, bydispersing carbon fillers into an elastic film used when the OLED isfixed to a lower frame, heat generated in the OLED can be efficientlyabsorbed. The absorbed heat is diffused to the lower frame to dissipatethe heat.

In the case of OLED of bottom emission method, in the sectionalstructure shown in FIG. 2, to extract heat generated in the structurepart of the OLED from the back surface of the light emitting side, theheat must be received across the empty wall (generally space filled withnitrogen), the desiccant, and the sealing glass. According to the heatdiffusion mechanism of this embodiment, since a heat transfer mechanismis used that absorbs infrared emission from a heating part of the OLEDto the elastic film, heat can be efficiently dissipated even in the OLEDof the bottom emission method that has difficulty in cooling. Table 1shows the specification of an elastic film having a cooling mechanism inthis embodiment. Although it is desirable that the elastic film isbonded to the OLED by self welding, use of general adhesive anddouble-faced tape provides sufficient performance (see FIG. 10).

<Table 1>

TABLE 1 Embodiment of special heat transfer film Layer configurationSilicon resin Material Silicon resin containing carbon filler, infraredabsorption ceramic, Ni powder, etc. Remarks Structure requiring noadhesives because of a mechanism of self welding to glass Heatabsorption based on infrared radiation by heat radiation rate of 0.80 ormore Heat transfer rate ≧1.0 W/(m · k)

<6. Cooling Mechanism>

(1) Since glass easily transmits infrared rays, by using a special heatcooling film of this proposal, heat generated in an OLED light emittingpart is absorbed by infrared rays across a sealing glass and transferredto a metallic frame.

(2) Although natural silicon resin is low in heat conductivity, heatradiation rate, and the like, the infrared absorption property and heatconductivity are improved by incorporating carbon black fillers andinfrared absorption ceramic for increasing a heat radiation rate and Nipowder for increasing heat conductivity into the silicon resin.

(3) By using metallic foil in an upper portion, heat generated in theresin of this proposal is conducted to the outside. In this case, asapplications, the heat may be conducted to near metallic housing, or theair may be cooled by exposure to the atmosphere. Table 2 compares anOLED cooling mechanism between a conventional one and the embodiment ofthe present invention.

<Table 2>

TABLE 2 Comparison of an OLED cooling mechanism between a conventionalone and the embodiment of the present invention Item This proposalConventional one Remarks Structure Silicon resin plus AL tape sticking Asticking surface metallic frame is the back of OLED. (sputter film isalso available) Heat absorption Infrared Infrared from a lightabsorption absorption emitting surface capacity is low because of heatradiation rate of 0.1 or less. Heat route during No heat resistance Anadhesive layer No heat resistance infrared layer exists is resistant tolayer exists absorption because no heat (heat because of Direct heatadhesive is used, cushion), and heat interface welding. conduction fromand heat is resistance sealing glass directly absorbed increases.(conducted) to silicon. Cooling mechanism Heat is conducted Heat isconducted for heat through metallic through AL foil. conduction toframes. external radiator When atmospheric Resin between Since anadhesive temperature is metallic frames layer is thin, higher than andOLED elements heat from metallic elements serves as heat foil conductsto cushion. the elements. Reliability The interface The adhesive layerwelding mechanism deteriorates with will not strip time because ofobjects once heat of the bonded together. elements. EMI property Sinceconductive Since the adhesive substance and layer generally dielectricexhibits contained in insulation and has silicon resin have no capacitya resistance component, it is component and a inadequate as a capacitycountermeasure component, they against EMI. can absorb electromagneticradiation.

1. An organic EL display device, wherein an OLED element is formed on asubstrate, and a sealing substrate of a structure by which the substrateis sealed is fixed to a lower metallic frame via an elastic sheet. 2.The organic EL display device of claim 1, wherein the sheet is formedfrom silicon resin.
 3. The organic EL display device of claim 3, whereinthe sheet has a heat diffusion function based on radiation.
 4. Anorganic EL display device, wherein a lower frame and an upper frame havean engagement structure by snap fit that has a notch shape.
 5. Theorganic EL display device of claim 4, wherein each side of the frameshas the notch shape.
 6. An organic EL display device, wherein wall partswith an upper frame and a lower frame combined and OLED panels are fixedin positions apart from each other.
 7. An organic EL display device,wherein a slope spring is provided in a lower frame and a support springis provided in an upper frame, and wherein OLED panels are fixed to thelower frame and the upper frame.
 8. The organic EL display device ofclaim 7, wherein the height of the joint surface of the upper and thelower springs is designed to be nearer to the light emitting surfacethan the position of the surface of FPC extraction to the OLED element.